1. Field of the Invention
The present invention relates to a starter device. More particularly, it relates to a starter device to start an automobile engine.
2. Discussion of Background
A known overhang type starter device is shown in FIG. 3, wherein a passage or opening 2 is formed in a front machine frame 1; a bearing 3 is fitted to the front machine frame 1 at a position inside the opening 2 and slidably supports a tubular pinion shaft; a rotary output shaft 4 is inserted as a supporting shaft in the tubular pinion shaft 5, and a pinion 5a is formed at the outer circumferential part of the front end of the pinion shaft 5 so that the pinion is engaged with a ring gear (not shown) of an engine when the pinion shaft is extended from the opening 2.
In FIG. 3, a d.c. motor 7 has an armature rotary shaft 6. A sun and planet gear speed reducing device 8 is provided with a plurality of planet gears 8b meshed with a sun gear 8a formed in the armature rotary shaft 6 so that a revolution speed of the rotary shaft 4 is reduced. A rotary output shaft 4 is disposed on the same axial line of the armature rotary shaft 6. One end of the rotary output shaft 64 constitutes a carrier 8c for the planet gear speed reducing device 8 and the other end is extended to the opening 2 of the front machine frame 1.
An overrunning clutch 9 is slidable on the rotary output shaft 4, which comprises a clutch outer member 9a meshed with a helical spline 4a formed on the rotary output shaft 4 and a clutch inner member 9b constituted by the rear end portion of a tubular pinion shaft 5. A rear bracket 10 is attached to the rear end portion of the yoke 7a of the d.c. motor 7. An electromagnetic switch 11 is mounted on the d.c. motor and attached to the upper part of the front machine frame 1. The electromagnetic switch 11 comprises an exciting coil 12 wound on a bobbin, a plunger 14 as a movable iron core, a rod 15 disposed in an insertion hole formed at the central portion of a fixed iron core 13 and extending toward the plunger 14, a movable contact 16 supported by the rod 15, a fixed contact 17, a return spring 18 interposed between the fixed iron core 13 and the plunger 14, and a hook 19 disposed in a recess formed in the plunger 14.
A shift lever 20 is pivotally supported in the front 25 machine frame 1 and has one end engaged with a retaining portion 19a of the hook 19 and the other end which is engaged with an annular member 21 attached to the clutch outer member 9a of the overrunning clutch 9. A numeral 22 designates a compression spring to apply a pushing force to the hook 19 so that a pinion 5a formed in the pinion moving shaft is engaged with the ring gear of the engine by means of the shift lever 20.
In the conventional starter device, a stopper 23 is fixed at the outer circumferential part of the front end (at the right side in FIG. 3) of the rotary output shaft 4. Further, an enlarged inner diameter portion 5b is formed at the front end of the tubular pinion moving shaft along a predetermined length in its axial direction, the length corresponding to the moving distance of the tubular pinion shaft 5. Accordingly, when the pinion shaft 5 is moved forwardly by the shift lever 20, a step portion 5c formed at the left of the enlarged inner diameter portion 5b of the pinion moving shaft 5 is brought to contact with the stopper 23 at a predermined position, i.e. the position where the pinion 5a is meshed with the ring gear of the engine, whereby the pinion shaft 5 is stopped. Thus, the entire length of the starter device can be shortened by forming the enlarged inner diameter portion 5b at the front end of the tubular pinion moving shaft 5 so that the stopper 23 is relatively moved in the large diameter portion 5b when the pinion moving shaft 5 is forwardly moved until the step portion 5c is brought to contact with the stopper 23.
In the conventional starter device having the construction decscribed above, the enlarged inner diameter portion 5b formed at the front end of the tubular pinion moving shaft 5 reduces the thickness of the bottom land of the pinion 5a. The reduced thickness of the bottom land causes limitations in the size and the number of teeth of the pinion 5a. In other words, the bottom land of the pinion 5a has to be sufficiently thick in order to maintain a sufficient strength of the pinion 5a. Accordingly, the size and the number of the teeth of the pinion has to be within the minimum requirements, and there is limitation with respect to the gear ratio of the pinion to the ring gear of the engine, whereby flexibility in designing the starter device is small. The electromagnetic switch in the conventional starter device is so constructed that the return spring 18 is interposed in a compressed state between the plunger 14 and the circumferential portion of the fixed iron core 13 so that the tubular pinion moving shaft 5 is returned to the retracted position by means of the shift lever 20. Accordingly, the cross-sectional surface area constituting a magnetic path is reduced to thereby reduce a magnetic attractive force of the plunger is reduced.